Non-symmetrical photo tooling and dual surface etching

ABSTRACT

The invention concerns photo etching processes to generate selected shapes and edges on finished articles. In particular, the invention relates to a process for generating sharp edges on blades and sharp edges on the teeth of graters. A non-symmetrical process of etching and photo tooling is employed to generate elongated sharpened edges.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns photo etching processes to generate selectedshapes and edges on finished articles. In particular, the inventionrelates to a process for generating sharp edges on blades and sharpedges on the teeth of graters. The methods of photo-tooling design andetching have been improved to achieve elongated cutting edges havingsuperior functional cutting characteristic while improving productivityin the manufacturing process.

2. Description of the Prior Art

U.S. Pat. No. 4,793,218 (Jordan et al.) teaches a method for formingknife blades from a flat section of pre-hardened metal including thesteps of photochemically etching a plurality of blanks from a section ofpre-hardened material so that each blank has a predetermined shape, andsharpening at least one edge of each blank by grinding. This prior artpatent teaches the use of photo etching techniques for the purpose offorming knife blades generally, but the process produces an etched shapewhich then requires further sharpening by grinding. This additionalprocess step increases manufacturing times and costs, and produces andproduces a lesser quality sharpened edge.

U.S. Pat. No. 5,317,938 (De Juan, Jr. et al.) teaches a method of makinga microsurgical cutter comprising the steps of forming a photo resistmask layer on the surface of a pattern for a microsurgical instrument,etching isotropically the top surface of the substrate through the topsurface to the bottom surface so that the top and bottom surfaces meetat a cutting edge portion with the cutting edge portion having aconfiguration corresponding to the edge portion of the mask layer. Aphoto lithographic mask is applied to both the upper and lower sides ofthe substrate and both sides are subjected to etching plasma. Theetching can be conducted simultaneously or sequentially depending uponthe desired etching process until the two surfaces meet and therebyproduce an edge portion which constitutes the knife edge.

U.S. Pat. No. 2,842,387 (Marcus) teaches the etching of knife bladeshaving exceptionally sharp cutting edges. The particular contours of thecutting edges are achieved by variable positioning of the photo resistmask layer which is applied to the knife surface. Additionally,sequential applications of mask layers and sequential photo etchingsteps are also applied to achieve desired blade contours. All of thesemethods appear to be employed in a system in which etching occurs fromone side only. Moreover, the manufacturing costs associated withsequential rounds of photo-etching treatments may be prohibitive in mostcommercial applications.

It is an object of the present invention to provide an improved chemicalmachining method for manufacturing sharpened edges on metal members forcutting tools, graters, and the like which overcomes the previouslymentioned shortcomings.

SUMMARY OF THE INVENTION

In accordance with the present invention, a method of manufacturing asharpened edge on a metal member of the type having a generally flat,first surface, an opposite second surface and a peripheral edge,comprises the steps of applying to the first surface of the metal membera first predetermined pattern of etching resistant material definingunprotected areas separated by resist areas, applying a second layer ofpredetermined pattern of etching resistant material to the secondsurface of the metal member at a selected alignment with a selectedportion of the resist areas on the first surface of the metal member.The next step is subjecting the first surface of the metal member to afirst etching treatment at a first selected rate, and simultaneouslysubjecting the second surface of the metal member to a second etchingtreatment at a second selected rate, which second selected rate does notequal the first selected rate. The method then requires continuing thefirst and second etching treatments to etch through the non-protectedareas on both surfaces of the metal member to form a sharpened edgeopposite the peripheral edge at a position variable with the ratio ofthe first to the second selected rates of etching treatment.

In a preferred embodiment of the present invention the ratio of thefirst to the second selected rates of etching treatment is approximately70:30.

The position of the sharpened edge relative to and opposite theperipheral edge may be shifted by adding the further step of continuingto simultaneously subject both sides of the metal member to said firstand said second etching treatments for a selected time after the metalmember has been etched through, so as to shift the sharpened edge towardthe second surface of the metal member.

In accordance with another preferred embodiment of the presentinvention, an elongated sharpened edge may be manufactured by thepresent method wherein the selected alignment of the second layer isoff-set from the selected portion of the protected areas on the firstsurface of the metal member;

Additional objects, features and advantages will be apparent in thewritten description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a schematic representation of a conventional dual sidedsymmetrical photo-etching process during application of the etchingtreatment to both the first and second surfaces of a metal member.

FIG. 1 b is a schematic representation of the edge obtained by theconventional symmetrical photo-etching process of FIG. 1 a;

FIG. 2 a is a schematic representation of a two sided asymmetricalphoto-etching process during application of the etching treatment toboth the first and second surfaces of a metal member in accordance withthe present invention.

FIG. 2 b is a schematic representation of the edge obtained by the twosided asymmetrical photo-etching process of FIG. 2 a;

FIG. 3 is graphic representation of the photo-tooling pin alignment.

FIG. 4 is a schematic representation of two sided symmetrical exposingprocess showing the alignment of the first and second layers of etchingresistant material being exposed in full alignment.

FIG. 5 is a schematic representation of two sided asymmetrical exposingprocess showing the alignment of the first and second layers of etchingresistant material being exposed in off-set alignment.

FIG. 6 is a schematic representation of the off-set alignment whichcould be used in the manufacture of sharpened edges on the teeth ofgraters;

FIG. 7 is a schematic representation of a cross-sectional view of aportion of a metal member and showing in dotted outline the shifting ofposition of the sharpened edge toward the plane of the second surface ofthe metal member in accordance with a preferred embodiment of thepresent invention.

FIG. 8 is a schematic representation of an elongated sharpened edgemanufactured in accordance with a preferred embodiment of the presentinvention;

FIG. 9 is a magnified photograph of an elongated sharpened edgemanufactured in accordance with a preferred embodiment of the presentinvention;

FIG. 10 is a magnified photograph of a sharpened edge manufactured by aconventional photo-etching process.

DETAILED DESCRIPTION OF THE INVENTION

The present invention utilizes chemical etching to produce sharpenededges on metal members. The word “members” is employed in thedescription and claims in order to convey the fact that the methods ofthe present invention are applicable to generating sharpened edges on ametal member of the type having a generally flat, first surface, anopposite second surface and a peripheral edge. These “members” wouldinclude knife blades, scalpel or other sharp instrument blades, theteeth of graters, files, saw blades, sharpened contoured openings, andcutters. Additionally, the methods of the present invention may haveapplication in other manufacturing processes where a sharpened edge isrequired. The processes of the present invention are equally applicableto the creation of sharpened edges on metal members which areessentially finished products once the methods have been carried out,and also to metal blanks which may require sharpened edges, but whichmay subsequently undergo further secondary processing in order tocomplete the manufacture of a finished product. For convenience and inaccordance with the custom in the industry, the word “blank” may be usedin the description, but the use of this word is not intended to limitthe scope of the present invention.

Chemical etching techniques are known in the art for making devices ortools having cutting teeth such as files, rasps, saw blades, and thelike. A metal blank is provided with those areas of the blank which areto form teeth, ridges or other cutting elements being selectively coatedwith a material which prevents the etching fluid from contacting andacting on them and other areas of the blank are left exposed for theetching treatment. The etching fluid first acts on the surface areaswhich are not protected by the resist material, and as the etchingproceeds, the material not protected by the resist is removed. Thepattern of the resist material which is coated on the blank is variedaccording to the character of the cutting elements that are desired. Forexample, a pattern of isolated areas where the etching is to start maybe formed in an otherwise continuous etching resist coating, or isolatedareas of the etching resist coating may be formed on the otherwiseexposed surface areas of the blank. The actual etching fluids and resistmaterials utilized will be familiar to those skilled in the art and donot form a part of the present invention.

FIG. 1 a represents the typical etching process, set up with a goal ofremoving material equally from the top vs. the bottom (50/50). Theresult is an even, minimized cusp feature 25, which is inherent to theetching process, and which is illustrated in FIG. 1 b. In general thecusp feature 25 is the result of the acid undercutting the photo-resistduring the etching process. This continues until the material breaksthrough from the top and bottom. It is typical for customers to requestthis feature to be minimized in many acid etched manufacturingapplications.

The method of the present invention is an asymmetrical dual-surfaceetching process. As shown in FIG. 2 a, a first layer of etchingresistant material 20 is applied to the first surface of 22 metal memberin a predetermined pattern, defining unprotected areas 24 of the metalmember's first surface separated by resist protected areas 26. A secondlayer of etching resistant material 28 is applied to the metal member'ssecond surface in a selected alignment with a selected portion of theresist areas on the first side of the member or blank. Accordingly,unprotected areas of the second surface are aligned with and overlie thecorresponding exposed areas on the first surface. An etching treatment,preferably an, acid etching spray shown by arrows in FIG. 2 a is thenapplied to both surfaces of the metal blank, etching away the exposedareas of both the back and front surfaces simultaneously. The exposedmetal is continually etched from both surfaces until the entirethickness of the metal is etched through.

The process of the present invention for creating sharpened edgesrequires the removal of more material from one side than the otherduring the etching process. The asymmetrical removal is a direct resultof the subjecting the first surface of the metal member to a firstetching treatment at a first selected rate and simultaneously subjectingthe second surface of the metal member to a second etching treatment ata second selected rate, which second selected rate does not equal thefirst selected rate. The ratio of the first to the second selected ratesof etching treatment should be greater than 55:45. A ratio of greaterthan 65:35 is preferred over lesser ratios. The most preferable ratio ofthe first to the second selected rates of etching treatment isapproximately 70:30. The etch ratio is being manipulated by changingvariables in the etching process. The primary variable adjusted is thespray pressures in the etching machine.

In accordance with the most preferred embodiment, the metal etched awayby the first surface etch treatment accounts for approximately 70% ofthe thickness of the metal blank while the second surface etchingtreatment accounts for the remainder of the metal blank surface, beingapproximately 30%. This change in etch ratio results in an increasedcusp 27 as shown in FIG. 2 b. This increased cusp facilitates achievingthe functional cutting characteristic on the ends of the teeth of thegraters after etching. This dual surface etching process results in theformation of a cutting edge located in “the interior” of the metalblank. This means that the cutting edge 27 is between the planes of thefirst 22 and second 30 surfaces. The etch ratio can be measured on abreakout tab designed in the metal sheet array which is undergoingetching treatment, therefore avoiding destructive measuring.

The typical process for photo-tooling design is to generate in-linealignment of masking images, top and bottom, that are pin alignedtogether, as shown in FIG. 3, for use in the etching process.

It accordance with the most preferred embodiment, a further elongatedsharpened edge can be produced by the method according to the presentinvention, which works as follows. First, photoresist is applied to ametal blank, substantially as shown in FIG. 5. The photoresist is thenexposed by a light source and is selectively masked by photo tooling, 22and 28 in a non-symmetrical predetermined pattern, leaving exposedresist on the top 20 and bottom 30 surfaces of the metal blank.Specifically the photoresist is exposed so that after developing, anoffset 32 exists between the photoresist layers on the top and bottomplanes of the metal blank. The exact dimension of the offset isestablished during the initial design and product testing. As will bediscussed in greater detail below, the length of the offset is designedto optimize the cutting edge characteristics and the technicaladvantages associated therewith.

EXAMPLE 1

By way of example, a metal blank having a thickness of 0.012 inches. Afirst and a second layers of etching resistant material are applied tothe respective first and second surfaces of the blank in apre-determined pattern and having a photoresist offset of 0.010 inchesis illustrated in FIG. 5. The tolerance currently used for control ofetch ratio is ±10%. On a 0.012″ material, etching is 0.0084″±0.0012″material from the top, and 0.0036±0.0012″ from the bottom.

The etching process requires simultaneously subjecting first surface ofthe metal blank to a first etching treatment at a selected rate and thesecond surface of the metal blank to a second etching treatment at asecond selected rate, wherein the second selected rate does not equalthe first selected rate. A preferred ratio of etching treatment rates isdetermined for the particular manufacturing application. The primaryvariable adjusted in order to determine the etching treatment ratio isthe spray pressures in the etching acid. It is preferred to apply theetching treatments to the first and second surfaces in a 70:30 ratio,achieved by applying acid spray pressures to the first and the secondsurfaces in a correlated ratio. When the etch ratio has been verified,the speed of the conveyor through the etching chamber is adjusted basedon measurements of final part configuration. The primary features usedfor control of the etching process are: the tooling holes, width oftooth, width of window, and height of window. After being exposed to theacid spray for a specified period of time, the acid spray will etchthrough the entire thickness of the metal blank and break through themetal blank from the top and bottom.

When the etching process of the present invention is practiced using theoff-set alignment of the second to the first predetermined patterns ofetching resistant material, the exact position of the cutting edge, orcusp 27, can be adjusted by varying the amount of time during which themetal blank is exposed to the acid etching spray. The longer the etchingspray is permitted to contact the metal blank the more “under-cutting”will occur behind the respective resists. As the under-cuttingcontinues, the metal is increasingly undercut and the position of thecusp moves closer to the plane edge of the blank. Thus if the acidetching spray is removed or neutralized immediately upon the acidetching “breaking through” the metal blank, the position of the cuspwithin the thickness of the blank will correlate relatively closely tothe ratio of etching from both sides. In other words, if the blank isacid etching spray is applied 70% from a first side and 30% from thesecond side of the blank until the acid “breaks through” and the metalblank is cut, and then the etching spray is immediatelyremoved/neutralized, the cusp will be at a position approximately 70% ofthe through the thickness of the blank, as best seen in FIG. 6. If theacid etching spray, applied in the same 70:30 ratio is allowed to remainin contact with the blank longer after the time of “break through”, theeffect of the acid etching spray will continue, causing undercuttingbehind the resist and effectively shifting the position of the cusptoward the plane of the second side of the metal blank, being the sidewhich received the lesser application of the acid etching spray.Accordingly the cusp may be shifted from a position at 70:30 to aposition approaching 90:10, or ultimately to a position at the plane ofthe second side of the blank. Thus, by varying the time of exposure tothe acid etching spray following breakthrough in accordance with thepresent invention, it is possible to selectively position the sharpenededge or cusp, even to the point of obtaining a sharpened edge in theplane of the second side, such as could only previously be produced by aprocess of etching solely from one side of the metal.

In accordance with the preferred embodiment, FIG. 7 illustrates theformation process by showing the cutting edge 27 at intervals of timeduring the etching process. From a time 0 to a time T1, the acid etchesthrough the metal until the acid etches through the entire thickness ofthe blank. This results in an off-plane cutting edge being formed at thepoint of breakthrough of the etching treatment through the metal member,is indicated by the cusp 27′ on the dotted line labeled T1. From time T1to time Ttot, the acid continues to be sprayed from both sides,contacting both the top and bottom of the initially formed off-planecutting edge (dotted line T1). As the acid continues the metal isundercut behind the second layer 28 of photo-resistant material. Thevertical position of the cutting edge gradually moves towards the bottomplane of the second surface 30 of the metal blank until time Ttot isreached. At time Ttot, the cutting edge 27″ becomes locatedapproximately the bottom plane. The acid spray is terminated and themetal blank is no longer etched. Thus, the in-plane cutting edge isbeing formed from etching taking place from both the top and the bottom.Thus, relative to the notional peripheral edge 12, the position of thecutting edge 27 can be shifted toward the second surface 30 of the metalmember 10.

A fully etched metal blank is shown in FIG. 8. As a result of theaforementioned etching process, two edges are formed in the metal blank.A cutting edge, and a non-cutting edge. The cutting edge 34 is formedfrom the exposed metal that is near the offset segment 32 of thephotoresist pattern. The non-cutting edge 36 is formed from the exposedmetal that is near the symmetric segment of the photoresist pattern. Forthe exemplified thickness, offset and material removal ratio, it isestimated that the non-cutting edge will be formed approximately 70%from the top plane and 30% from the bottom plane, while the cutting edgewill be formed approximately 85% from the top plane and 15% from thebottom plane.

The cutting edges formed by the offset etching process of FIG. 8 resultsin cutting edges having superior length and incline anglecharacteristics that can not be achieved by using a single side etchingprocess. The dual-side etching process decreases manufacturing timewhich results in a considerable economic advantage, which provides asuperior elongated cutting edge. Reference may be had to FIGS. 9 and 10to illustrate the differences between an elongated sharpened edgeaccording to the present invention and an edge produced by conventionalsingle sided etching. The method of the preferred embodiment of thepresent invention results in a sharpened edge which has a greater length(0.0109 inches) than (0.0042 inches) the conventional edge in thepresent example. The sharpened edge manufactured in accordance with thepresent invention can be easily tailored to an application to optimizethe length of the cutting edge, sharpness and resistance to wear.

The invention has been provided with several advantages. Thephotochemically machined cutting tools of the invention have toothshapes which can be made in any conceivable size, shape or patternwithout the use of expensive dies or fixtures. The cutting edges of thetooth shapes are razor sharp, without the necessity of grinding orhoning. The cutting tools of the invention are well adapted for use assheet metal cutting tools including circular and linear wood cutting sawblades, micro-planing blades for hand tools and micro-planing blades forpower tools. The files and cutters produced by the method of theinvention have teeth with associated slots for removal of material fromthe work surface. The cutters and files made by the method of theinvention are thinner, more flexible, sharper and less likely to loadthan those made with the prior art techniques. While the invention hasbeen shown in only one of its forms, it is not thus limited but issusceptible to various changes and modifications without departing fromthe spirit thereof.

1. A method of manufacturing a sharpened edge on a metal member of thetype having a generally flat, first surface, an opposite second surfaceand a peripheral edge, the method comprising the steps of: a. applyingto the first surface of the metal member a first predetermined patternof etching resistant material defining non-protected areas separated byresist areas; b. applying a layer second predetermined pattern ofetching resistant material to the second surface of the metal member ata selected alignment with a selected portion of the protected areas onthe first surface of the metal member; c. subjecting the first surfaceof the metal member to a first etching treatment at a first selectedrate; d. simultaneously subjecting the second surface of the metalmember to a second etching treatment at a second selected rate, whichsecond selected rate does not equal the first selected rate; and, e.continuing the first and second etching treatments to etch through theexposed areas on both surfaces of the metal member to form a sharpenededge opposite the peripheral edge at a position variable with the ratioof the first to the second selected rates of etching treatment.
 2. Themethod of claim 1 wherein the ratio of the first to the second selectedrates of etching treatment Is greater than 55:45.
 3. The method of claim2 wherein the ratio of the first to the second selected rates of etchingtreatment is greater than 65:35.
 4. The method of claim 3 wherein theratio of the first to the second selected rates of etching treatment isapproximately 70:30.
 5. The method of claim 1 wherein the ratio of thefirst to the second selected rates of etching treatment is achieved byapplying elected unequal acid spray pressures to the first and thesecond surfaces.
 6. The method of claim 1 wherein the selected alignmentof the second predetermined pattern of etching resistant material isinline alignment with the selected portion of the resist areas on thefirst surface of the metal member.
 7. The method of claim 6, wherein theselected alignment of the second predetermined pattern of etchingresistant material is off-set alignment from the selected portion of theresist areas on the first surface of the metal member.
 8. The method ofclaim 7, further comprising a step of: continuing to simultaneouslysubject both sides of the metal member to said first and said secondetching treatments for a selected time after the metal member has beenetched through, so as to shift the sharpened edge toward the secondsurface of the metal member.
 9. A method of manufacturing an elongatedsharpened edge on a metal member of the type having a generally flat,first surface, an opposite second surface and a peripheral edge, themethod comprising the steps of: a. applying to the first surface of themetal member a first predetermined pattern of etching resistant materialdefining un-protected areas separated by resist areas; b. applying alayer second predetermined pattern of etching resistant material to thesecond surface of the metal blank at a selected alignment being off-setfrom the selected portion of the resist areas on the first surface ofthe metal member; c. subjecting the first surface of the metal member toa first etching treatment at a first selected rate; d. simultaneouslysubjecting the second surface of the metal member to a second etchingtreatment at a second selected rate, wherein the ratio of the firstselected rate to the second selected rate is approximately 70:30; e.continuing the first and second etching treatments to etch through theexposed areas on both surfaces of the metal member to form an elongatedsharpened edge opposite the peripheral edge at a position variable withthe ratio of the first to the second selected rates of etchingtreatment.
 10. The method of claim 9, further comprising a step of: f.continuing to simultaneously subject both sides of the metal member tosaid first and said second etching treatments for a selected time afterthe metal member has been etched through to shift the position of theelongated sharpened edge toward the second surface of the member.
 11. Asharpened edge on a metal member of the type having a generally flat,first surface, an opposite second surface and a peripheral edge, whichsharpened edge is manufactured by the steps of: a. applying to the firstsurface of the metal member a first predetermined pattern of etchingresistant material defining non-protected areas separated by resistareas; b. applying a layer second predetermined pattern of etchingresistant material to the second surface of the metal member at aselected alignment with a selected portion of the resist areas on thefirst surface of the metal member; c. subjecting the first surface ofthe metal member to a first etching treatment at a first selected rate;d. simultaneously subjecting the second surface of the metal member to asecond etching treatment at a second selected rate, which secondselected rate does not equal the first selected rate; and, e. continuingthe first and second etching treatments to etch through thenon-protected areas on both surfaces of the metal member to form asharpened edge opposite the peripheral edge at a position variable withthe ratio of the first to the second selected rates of etchingtreatment.
 12. The sharpened edge according to claim 11 wherein thesharpened edge is positioned adjacent the second surface of the metalmember by the additional step of f. continuing to simultaneously subjectboth sides of the metal member to said first and said second etchingtreatments for a selected time after the metal member has been etchedthrough to shift the position of the elongated sharpened edge toward thesecond surface of the member.
 13. The sharpened edge according to claim9 or 11 wherein the sharpened edge is elongated by applying the secondpredetermined pattern of etching resistant material to the secondsurface of the metal member at a selected alignment which is off-setfrom the selected portion of the first predetermined pattern of etchingresistant material.